She has a lot of nerve to lecture you about your marriage and she's not even your husband's girlfriend! She's some lady he was flirty-chatting with online that he met for coffee ONCE. If this is how she is NOW, can you imagine having her in your life if only vicariously? What a good thing she doesn't know your last name or where you live! But I'd watch out because you can track people down through their cell phone number. There are websites that do it for a small fee. If she's as screwy as she sounds I wouldn't put it past her to resort to "self-help". You know what they say about women scorned (I think it applies to men sometimes too).
It sounds like she'd be a better match for a man who is also cheating on his wife, not for a man who is trying to establish a "polyamorous" lifestyle.